Dick Hill is Jack Reacher for audiobook fans. Hill narrated the last 18 of the 22 books in this Lee Child series. Although he missed books two through four, he spoke at the genesis with the first Reacher book, “Killing Floor.” So it pains me to say this, but: It’s time for Hill to go. Somewhere around book 19, “Personal,” Hill’s voice developed a warble. With each successive novel, Reacher sounds less like a tough guy and more like someone’s uncertain grandpa. The problem is more of tone than age. There is little in the books to remind us that Reacher, who fights with the ferocity and experience of a 30-something brawler, is actually 57. But Hill’s narration turns him geriatric. While it is delightful to imagine pops taking on seven outlaw bikers — none of whom so much as scuffs his shoes — it strains even my very elastic credulity when it comes to Jack Reacher. (I also miss the days when Reacher still took an occasional punch.)

More problematic: It’s often difficult to tell who’s talking. Is it Reacher or the private investigator he’s teamed with? Is it Reacher or the general who runs West Point? They are frequently indistinguishable. You can regain a younger Reacher if you speed the playback to 1.25x on your smartphone, but that doesn’t fix the dialogue confusion. Hill is a celebrated narrator, with more than 500 titles to his name and three Audie awards. He’s earned his place among the great voices. But for Jack Reacher, his voice is great no longer.